In various industries including the semiconductor manufacturing, a need exists for multifunctional, high-quality thin films (e.g., highly insulative thin films, semiconductor thin films, highly dielectric thin films, light-emitting thin films, highly magnetic thin films, and superhard thin films).
For example, in the manufacturing of semiconductor devices, films for use in semiconductor chips include a highly conductive film with a low impedance that corresponds to circuit wiring, a highly magnetic film that functions as a wiring coil of a circuit or as a magnet, a highly dielectric film that functions as a capacitor in a circuit, and a highly insulative film that causes a less amount of electrical leakage current.
Examples of techniques that have been used to form these film include the thermal chemical vapor deposition (CVD) apparatus, the photo CVD apparatus, and the plasma CVD apparatus. Particularly, the plasma CVD apparatus has been commonly used. As compared to the thermal and photo CVD apparatuses or the like, the plasma CVD apparatus can lower the temperature of film formation and increase the speed of film formation, so that a film formation process can be accelerated.
For example, the following technique that uses the plasma CVD apparatus is generally employed to form, on a semiconductor substrate, a gate insulation film such as a nitride film (e.g., SiON or HfSiON) or an oxide film (SiO2 or HfO2).
Thus, a gas of NH3 (ammonia), N2, O2, O3 (ozone), or the like and a precursor gas of silicon, hafnium, or the like are directly supplied to a process chamber apparatus in which the CVD process is to be performed. In the process chamber apparatus, the precursor gas is dissociated to form metal particles, and then, a thin film such as a nitride film or an oxide film is formed on a target object by a chemical reaction between the metal particles and the above-mentioned gas of NH3 (ammonia) or the like.
In the plasma CVD apparatus, high-frequency plasma or microwave plasma is directly generated in the process chamber apparatus. The target object is accordingly exposed to a radical gas or plasma ions (or electrons) having a high energy.
Patent document 1 is an example of related art documents in which techniques associated with plasma CVD apparatuses are disclosed.
In the film formation process performed in the plasma CVD apparatus, the target object is directly exposed to plasma, as mentioned above. The target object is heavily damaged by plasma (ions or electrons), so that the performance of a semiconductor function suffers.
In contrast, in the film formation process using the thermal and photo CVD apparatuses, the target object is not damaged by plasma (ions or electrons), and a high-quality film such as a nitride film or oxide film is formed accordingly. In such a film formation process, however, it is difficult to provide a large amount of highly concentrated radical gas source and it accordingly takes a very long time to form a film.
The recent thermal and photo CVD apparatuses use, as a source gas, an HN3 gas or a O3 gas, which is highly concentrated and readily dissociated by radiation of heat or light. In a CVD chamber apparatus, a thermal catalyst is provided. Thus, a catalytic action promotes dissociation of the gas in the thermal and photo CVD apparatus, whereby a film such as a nitride film or an oxide film can be formed in a short time. However, this saves only a limited amount of time, and thus, it is difficult to accelerate the film formation significantly.
An example of apparatuses that can reduce damages to the target object caused by plasma and can further accelerate the film formation is a film formation process apparatus of remote plasma type (see, for example, Patent Document 2).
According to the technique disclosed in Patent Document 2, a plasma generation region and a target object process region are separated by a partition (plasma confining electrode). Specifically, according to the technique disclosed in Patent Document 2, the plasma confining electrode is located between a high-frequency application electrode and a counter electrode on which a target object is placed. The technique disclosed in Patent Document 2 provides the target object with only neutral activated species.
According to the technique disclosed in Patent Document 3, part of a source gas is activated by plasma in a remote plasma source. In the remote plasma source, a gas channel circles around in a loop. An active gas generated in the remote plasma source is discharged and supplied to the apparatus in which a target object is placed.
Various source gases such as a nitrogen gas, an oxygen gas, an ozone gas, or a hydrogen gas may be used in the thin film technique according to Patent Document 3 and the like. An activated radical gas is generated from the source gas, and then, a thin film is formed on a target object through the use of the radical gas.
The radical gas is highly reactive. The radical gas in minute quantities (at a concentration less than or equal to about 1%: 10000 ppm) is sprayed onto a target object to promote a chemical reaction in the target object, whereby a film such as a nitrogen thin film, an oxide thin film, or a hydrogen-reduced film (a metal film with enhanced hydrogen bonding) can be efficiently formed in a short time.
A radical generation apparatus includes discharge cells. In the discharge cells, high-field plasma is created through the use of a dielectric barrier discharge, which is atmospheric pressure plasma. Consequently, a high-quality radical gas is generated from the source gas exposed to the plasma in the discharge cells.